Hot Science - Cool Talk # 18 Supermassive Black Holes: Monsters

Dr. John Kormendy April 19, 2002

Produced by and for Hot Science - Cool Talks by the Environmental Science Institute. We request that the use of these materials include an acknowledgement of the presenter and Hot Science - Cool Talks by the Environmental Science Institute at UT Austin. We hope you find these materials educational and enjoyable. Supermassive Black Holes in Galactic Nuclei John Kormendy Curtis T. Vaughan, Jr. Centennial Chair in Department of Astronomy, University of Texas at Austin April 19, 2002

What are black holes? Why are we looking for them? The search for supermassive black holes Supermassive black holes and galaxy formation

Suppose we squeeze a planet of fixed mass M into smaller and smaller volumes.

The surface gravity gets bigger as you make the planet smaller. Surface gravity is proportional to 1/radius2.

m m GMmm weight = radius 2

Styrofoam low-gravity planet (big radius) 2GM radius= 2 Rock Lead c medium-gravity high-gravity planet planet radius (small) A black hole is so small fixed mass M M M that its surface gravity is so high that nothing can escape, not even light.

To turn the into a black hole, we would have to squeeze it into the size of a grape. Two Types of Black Holes

Black holes with masses of a few are well understood. The most massive stars turn into such black holes when they die in explosions.

Our Galaxy

These are millions of stellar-mass black holes — dead stars — scattered throughout the disk of our Milky Way galaxy. : Black Hole Mass = 1 Billion Suns

ESO Two Types of Black Holes Supermassive black holes with masses of a million to a few billion Suns live in galactic centers. We understand some of what they Orbit of Jupiter do, but we don’t know where they come from.

Orbit of Mars The Discovery of The identification by (1963, Nature, 197, 1040) of the radio source as a 13th “star” with a of 16 % of the speed of light was a huge shock. The Hubble law of the expansion of the Universe implies that 3C 273 is one of the most distant objects known. It must be enormously luminous. Quasars — violently active galactic nuclei — are the most luminous objects in the Universe, more luminous than any galaxy. The energy requirements for powering quasars were the first compelling argument for black hole engines.

3C 273 The Discovery of Quasars The identification by Maarten Schmidt (1963, Nature, 197, 1040) of the radio source 3C 273 as a 13th magnitude “star” with a redshift of 16 % of the speed of light was a huge shock. The Hubble law of the expansion of the Universe implies that 3C 273 is one of the most distant objects known. It must be enormously luminous. Quasars — violently active galactic nuclei — are the most luminous objects in the Universe, more luminous than any galaxy. The energy requirements for powering quasars were the first compelling argument for black hole engines.

3C 273 Many radio and quasars have jets that feed lobes of radio emission

Cygnus A Supermassive Black Holes as Engines Let’s try to explain quasars using nuclear reactions like those that power stars: • The total energy output of a quasar is at least the energy stored in its radio halo ≈ 1054 Joule.

• Via E = mc2, this energy “weighs” 10 million Suns.

• But nuclear reactions have an efficiency of only 1 %. • So the waste mass left behind in powering a quasar is 10 million Suns / 1 % ≈ 1 billion Suns. • Rapid brightness variations show that a typical quasar is no bigger than our Solar System. • But the gravitational energy of 1 billion Suns compressed inside the Solar System ≈ 1055 Joule.

“Evidently, although our aim was to produce a model based on nuclear fuel, we have ended up with a model which has produced more than enough energy by gravitational contraction. The nuclear fuel has ended as an irrelevance.”

Donald Lynden-Bell (1969)

This argument convinced many people that quasar engines are supermassive black holes that swallow surrounding gas and stars. Why Jets Imply Black Holes — 1

HST Jets remember ejection directions for a long time. This argues against energy sources based on many objects (supernovae). It suggests that the engines are rotating gyroscopes - rotating black holes. Why Jets Imply Black Holes — 2

HST Jet knots move at almost the speed of light. This implies that their engines are as small as black holes. This is the cleanest evidence that quasar engines are black holes. Why Jets Imply Black Holes — 2

Jet knots in M87 look like they are moving at 6 times the speed of light (24 light years in 4 years).

Biretta et al. 1999 This means that they really move at HST more than 98 % of the speed of light.

QuickTime™ and a decompressor are needed to see this picture. Supermassive Black Holes as Quasar Engines

QuickTime™ and a decompressor are needed to see this picture.

The huge and tiny sizes of quasars can be understood if they are powered by black holes with masses of a million to a few billion Suns.

Gas near the black hole settles into a hot disk, releasing gravitational energy as it spirals into the hole.

Magnetic fields eject jets along the black hole rotation axis. A black hole lights up as a quasar when it is fed gas and stars.

QuickTime™ and a decompressor are needed to see this picture. How do you feed a quasar ?

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Simulation: Josh Barnes

One possible answer: Galaxy collisions and mergers dump gas into the center. PROBLEM

People believe the black hole picture. They have done an enormous amount of work based on it.

But for many years there was no direct evidence that supermassive black holes exist.

So the search for supermassive black holes became a very hot subject.

Danger: It is easy to believe that we have proved what we expect to find. So the standard of proof is very high. The Quasar Era Was More Than 10 Billion Years Ago

Schmidt, Schneider & Gunn 1991, in The Space Distribution of Quasars (ASP), 109

Quasars were once so numerous that most big galaxies had one.

Since almost all quasars have now switched off, dead quasar engines should be hiding in many nearby galaxies. Now The Search For Supermassive Black Holes

The image shown here in the lecture is not available for public distribution. Canada-France-Hawaii-Telescope

QuickTime™ and a Cinepak decompressor are needed to see this picture. QuickTime™ and a Cinepak decompressor are needed to see this picture. Simple Spectrograph

Collimating Prism lens

Image of slit without prism

Slit Detector The telescope focuses light Camera lens on the slit. Red image Green image Blue image M 31: Black Hole Mass = 40 Million Suns

M 31 on spectrograph slit

Spectrum of M 31 The brightness variation of the galaxy has been divided out. Position along slit The zigzag in the lines is the signature of the rapidly rotating nucleus and central black hole. Red Blue M 31: Black Hole Mass = 40 Million Suns

Kormendy & Bender 1999, ApJ, 522, 772 random speedrandom (km/s) rotationspeed (km/s)

distance from center (arcseconds) M 31: Black Hole Mass = 40 Million Suns Distance ≈ 2.5 x 106 light years (ly) ⇒ scale = 82 arcsec / 1000 ly.

Observe rotation velocity V ≈ 160 km/s at radius r = 1 arcsec.

Mass: Balance centripetal acceleration and gravity: mV2/r = GMm/r2 ⇒ M = V2 r / G , where M = central (“black hole”) mass; m = mass of orbiting star; G = Gravitational constant; = 6.673 x 10-8 cm3 / g s2.

Approximate mass (160 km/s)2 (105 cm / km)2 (1 arcsec) (9.47 x 1017 cm/ly) V2 r / G ≈ ———————-——————————————————————- -8 3 -1 -1 33 (6.673 x 10 cm g s ) ( 1.99 x 10 g/ M) (82 arcsec / 1000 ly)

6 = 22 x 10 M . This is an underestimate because it does not include the effects of projection or random velocities. M 31: Black Hole Mass = 40 Million Suns

HST NGC 3115: Black Hole Mass = 1 Billion Suns NGC 3115: Black Hole Mass = 1 Billion Suns

NGC 3115 has a bright central cusp of stars like we expect around a black hole. Stars in this nuclear cluster move at about 1000 km/s. But: if the nucleus contained only stars and not a black hole, then its escape velocity would be 350 km/s. Stars moving at 1000 km/s would fly away.

This shows that the nucleus contains a dark object of mass 1 billion Suns. The Nuker Team

Additional Nukers Gary Bower Luis Ho John Magorrian Jason Pinkney Tod Lauer Doug Richstone Karl Gebhardt Scott Tremaine

Sandra Faber

John Kormendy

Alan Dressler

Thanks Also To STIS Team Members Gary Bower Ralf Bender Mary Beth Kaiser Charlie Nelson Alex Filippenko Richard Green Black Hole Census — April 2002

Galaxy Distance Black Hole Mass Galaxy Distance Black Hole Mass (million ly) (million Suns) (million ly) (million Suns)

Milky Way 0.028 3 NGC 5128 6.5 200 M 31 2.3 40 NGC 2787 42 71 M 32 2.3 3 M 87 52 2500 M 81 12.7 68 NGC 4350 55 600 NGC 3115 32 1000 NGC 4459 55 73 NGC 4594 32 1000 NGC 4596 55 78 NGC 3379 34 100 NGC 4374 60 1000 NGC 3377 37 100 IC 1459 95 200 NGC 1023 37 39 NGC 4261 104 540 NGC 3384 38 14 NGC 7052 192 330 NGC 4697 38 120 NGC 6251 345 600 NGC 7457 43 3 NGC 4564 49 57 NGC 4945 12.1 1 NGC 4342 50 300 NGC 4258 23 42 NGC 4486B 50 500 NGC 1068 49 17 NGC 4742 51 14 NGC 4473 51 100 NGC 4649 55 2000 Kormendy et al. NGC 2778 75 20 Gebhardt et nuk. NGC 3608 75 110 STIS GTO Team NGC 7332 75 15 NGC 821 78 50 NGC 4291 85 250 NGC 5845 85 320 M 87: Black Hole Mass = 2.5 Billion Suns

M 87 was observed with Hubble by Harms, Ford, and collaborators. 1150 km/s

From the difference in Doppler shifts seen on opposite sides of the center, the disk rotates at almost 600 km/s. This implies a black hole of mass 2.5 billion Suns. M 84: Black Hole Mass = 1 Billion Suns

The Space Telescope Imaging Spectrograph is providing spectacular new data on black holes.

Bower et al. 1998, ApJ, 492, L111 We observe only a shadow of the dark object — its gravitational effect on ordinary stars and gas. Are we detecting one object? Or two? Or many? Could we be detecting a cluster of dark stars?

Possibilities Brown dwarf stars White dwarf stars Neutron stars Stellar-mass black holes NGC 4258: Our Galaxy: Dark Mass = 42 Million Suns Dark Mass = 3 Million Suns

We can measure the rotation of these two galaxies especially close to the center. The dark mass is in such a small volume at the center that alternatives to a black hole (failed stars or dead stars) are ruled out. These are the best black hole candidates. Have we discovered black holes in galactic nuclei?

Probably.

Other alternatives are very implausible.

But: Absolute proof requires that we see velocities of almost the speed of light from near the surface of the black hole.

Nandra et al. 1997, ApJ, 477, 602 X-ray observations of Seyfert galaxies show spectral lines as wide as 100,000 km/s.

This is 1/3 of the speed of light. The image shown here in the lecture is not available for public distribution. The bulgeless galaxy M 33 does not contain a black hole. Typical stars in the nucleus of M 33 move at only 21 km/s. Any black hole must be less massive than 1500 Suns. Conclude: Every galaxy that contains a bulge component also contains a black hole. Conclude: Every galaxy that contains a bulge component also contains a black hole. Conclude: Every galaxy that contains a bulge component also contains a black hole. No bulge ⇒ no black hole. Black Hole Conclusions

Black hole masses are just right to explain the energy output of quasars. Black Hole Census — April 2002

Galaxy Distance Black Hole Mass Galaxy Distance Black Hole Mass (million ly) (million Suns) (million ly) (million Suns)

Milky Way 0.028 3 NGC 5128 6.5 200 M 31 2.3 40 NGC 2787 42 71 M 32 2.3 3 M 87 52 2500 M 81 12.7 68 NGC 4350 55 600 NGC 3115 32 1000 NGC 4459 55 73 NGC 4594 32 1000 NGC 4596 55 78 NGC 3379 34 100 NGC 4374 60 1000 NGC 3377 37 100 IC 1459 95 200 NGC 1023 37 39 NGC 4261 104 540 NGC 3384 38 14 NGC 7052 192 330 NGC 4697 38 120 NGC 6251 345 600 NGC 7457 43 3 NGC 4564 49 57 NGC 4945 12.1 1 NGC 4342 50 300 NGC 4258 23 42 NGC 4486B 50 500 NGC 1068 49 17 NGC 4742 51 14 NGC 4473 51 100 NGC 4649 55 2000 NGC 2778 75 20 NGC 3608 75 110 NGC 7332 75 15 NGC 821 78 50 NGC 4291 85 250 NGC 5845 85 320 

Kormendy 1993 Gebhardt et nuk. 2000; Ferrarese & Merritt 2000

Bigger black holes live Bigger black holes live in bigger galaxy bulges. in bulges in which the stars move faster. 

Black hole mass ≈ 0.2 % of bulge mass.

Bulge mass x constant

These diagrams contain almost the same information, because galaxy mass is measured by stellar velocity. What is new in the right panel? Answer: how much the bulge collapsed when it formed. 

Black hole mass ≈ 0.2 % of bulge mass.

Bulge mass x constant

Black hole mass is more connected with how much a bulge collapsed than with how big the bulge is. So there is a close connection between black hole growth and bulge formation. CONCLUSION The formation of bulges and the growth of their black holes, when they shone like quasars, happened together. This unifies two major areas of extragalactic research: quasars and galaxy formation.

Hubble Deep Field The Future

Short-term It should be possible to derive black hole masses for thousands of quasars and other active galaxies and probe the growth of black holes as the Universe evolved.

Long-term Gravitational wave astronomy THANKS

To Mr. And Mrs. Curtis Vaughan for endowing the Curtis T. Vaughan Centennial Chair in Astronomy.

To my wife Mary for putting up with an astronomer husband.

To Pamela Gay for her help with this presentation.

To the Nuker team and especially Karl Gebhardt for many years of fruitful collaboration. Dr. John Kormendy Department of Astronomy

Dr. John Kormendy is a professor at the University of Texas at Austin. His research interests include the search for black holes in galactic nuclei, elliptical galaxies and bulges of disk galaxies, dark matter, and secular evolution in galaxy structure.